Evelynn Ult Suggestion

Active: Evelynn impales all enemy units in the targeted area, dealing magic damage equal to a percentage of their current health and slowing their movement speed for 2 seconds.
Evelynn siphons their pain, gaining a shield that grows in strength for each enemy champion hit and lasts up to 6 seconds.

Current Health to Damage Ratio: 15% / 20% / 25% (+ 1% per 100 AP)

Shield Strength per champion hit: 150 / 225 / 300

Maximum Shield Strength: 750 / 1125 / 1500

Slow: 30% / 50% / 70%

Diameter of AoE: 500

*My Suggestion

Agony's Embrace

RANGE: 700

COST: 100 mana

COOLDOWN: 150 / 125 / 100

Active: Evelynn impales all enemy units in the targeted area, dealing base magic damage in addition to bonus damage equal to 15% their current health and slowing their movement speed by 50% for 2 seconds.
Evelynn siphons their pain, gaining a shield that grows in strength for each enemy champion hit and lasts up to 5 seconds.